I put the 6" bergstroms on my 06 Fusion 600. Stock track (not ripsaw, etc.) and no studs. I've been really happy with them although previously I just had the stock bars on and I haven't compared them to any real competitors. With the 6" bergstroms and the stock track, there is almost two much grip upfront as the back end has more of a tendency to slide in the turns. I think the 6" bars would be well-matched to your 136" track. I think I have about 2500 miles on them and they are holding up well so far.
I also got the shims, which lessened the steering effort fairly dramatically. I had a hard believing a little piece of plastic made such a difference.